Introduction of inert gas(at the same temperature) will affect the equilibrium if:

The correct option is (2) Pressure is constant and △ng≠0
1) Addition of inert gases at constant volume, increases the total pressure of the reaction mixture, however the partial pressure of the individual reactants is constant and hence does not have any effect.
2) Addition of inert gases at constant pressure, decreases the the partial pressures of the individual reactants and increases the volume. Hence the equilibrium is shifted towards the side where there is more number of moles.
3) and 4) addition of inert gases for the reaction for which △ng=0, will not have any effect on the equilibrium, since both the the sides are equally affected.